An image forming apparatus configured to electro-photographically form an image, such as a laser printer includes a low-voltage circuit which lowers a commercial voltage (for example, 100 V) from an external power source such as a plug to a predetermined low voltage, a main control circuit which receives supply of an electric power from the low-voltage circuit, controls various devices, and performs control on an image forming process of the image forming apparatus, and a high-voltage generator circuit which generates a high voltage and supplies an electric power to devices requiring a high-voltage power source, such as chargers and transfer units, and so on. Also, various boards used for configuring those circuits are disposed at predetermine positions of the image forming apparatus.
Recently, reduction of the size of image forming apparatuses is highly demanded. In reducing the size of image forming apparatuses, the way of arranging those boards is an issue, and a technique is proposed in, for example, JP-A-2007-152609. That is, in the technique of JP-A-2007-152609, a first electric board including a high-voltage generator circuit and a second electric board configuring a main control circuit are overlapped on one side surface of an image forming apparatus such that the first and second electric boards are arranged in parallel and close to each other. According to this configuration, for example, as compared to a case of arranging the boards on two sides of the image forming apparatus such that the boards face each other, it is possible to concentrically arrange the boards. Therefore, it is possible to reduce the size of the image forming apparatus, and make an interface between the boards shorter.
However, if the boards are simply arranged to overlap and be close to each other, the following problems occur. That is, since the boards are concentrically arranged in a limited region, that is, one side surface of the image forming apparatus, electric radiation noise, heat, or the like generated at each board may cause each board to abnormally operate, and electric radiation noise leaked from the boards to the outside may influence external devices.
Particularly, the high-voltage generator circuit includes a transistor which serves as a switching element to be turned on or off for controlling an electric current, a transformer which generates a back electromotive force to increase a voltage, and so on. Therefore, if the board of the main control circuit is overlapped on the board of the high-voltage generator circuit configured as described above, a possibility that the main control circuit having an important role will directly receive electric radiation noises generated from the transistor or the transformer of the high-voltage generator circuit and malfunction increases. Also, the electric radiation noise generated from the board of the main control circuit may be leaked to the outside and influence external devices or the like arranged closely.
For this reason, it may be conceivable to provide a countermeasure on the boards to shield electric radiation noise, heat, and the like, for example, by additionally providing a shield plate. In this case, the boards increase in size, and thus it may be difficult to contribute to size-reduction of the image forming apparatus.